Update: there is now a video of the announcement of the new brigade. Note Salahuddin Shishani’s presence:

JMA considers itself a branch of the Caucasus Emirate in Syria. It is not clear what prompted the merger — but it is worth noting that it comes after several weeks of little news from JMA, following the group’s advances in Layramoun, northwestern Aleppo, in previous months. It could be that the faction was depleted in heavy clashes with Assad’s forces. It is not clear yet who the Emir of the new group will be — i.e. if it will be JMA Emir Salahuddin Shishani or another leader; and it is also not clear to what extent JMA will maintain its relationship with the Caucasus Emirate following this move.